Method for ejecting ink droplets from a nozzle in a fill-before-fire mode

Abstract

A driving method for driving an ink ejection device operated in shear mode. In order that the ink ejection speed does not vary depending on the driving frequency, a first pulse signal and a second pulse signal are sequentially applied to the electrode of an ink channel. The first pulse signal is for ejecting an ink droplet from the corresponding nozzle of the ink channel, and the second pulse signal is for canceling pressure fluctuations remaining in the ink after ejection of ink. The second pulse signal has a voltage level equal to that of the first pulse signal. At the rising edge of the first pulse signal, the volume of the ink channel is increased from a natural volume to an increased volume. As a result, a pressure wave is generated in the ink filling the ink channel. At the falling edge of the first pulse signal, the volume of the ink chamber reverts to the natural volume, thereby ejecting an ink droplet from the nozzle. Thereafter, the second signal is applied to cancel out the residual pressure fluctuations. In the present invention, the sequential timings of the first and second pulse signals including the durations of the first and second pulse signals are specifically defined based on evaluation of experimental results.

What is claimed is: 
     
       1. A method of driving an ink ejection device having walls, a nozzle plate, an actuator and control means, the walls defining an ink channel, the ink channel having a volume filled with ink and having a length defined by two ends, the nozzle plate attached to one end of the ink channel and formed with a nozzle, the actuator operable for changing the volume of the ink channel, and the control means, operable in association with a single power source, for applying pulse signals to the actuator, the method comprising the steps of: (a) applying a first pulse signal to the actuator at a first timing To so that the volume of the ink channel is increased from a natural volume to an increased volume, the first ink channel, a time duration T being required for the pressure wave to propagate from one end to the other end in a lengthwise direction of the ink channel;   (b) stopping the application of the first pulse signal to the actuator at a second timing Tp after expiration of a predetermined duration of time given by multiplying an odd number equal to or greater than three to the time duration T so that the volume of the ink chamber reverts to the natural volume, thereby ejecting an ink droplet from the nozzle, a duration of the first pulse signal being defined by a duration of time from the first timing To to the second timing Tp;   (c) applying a second pulse signal to the actuator at a third timing Ts so that pressure fluctuations remaining in the ink are canceled out, the second pulse signal having a voltage level equal to the voltage level of the first pulse signal; and   (d) stopping the application of the second pulse signal to the actuator at a fourth timing Te, a duration of the second pulse signal being defined by a duration of time from the third timing Ts to the fourth timing Te and differing from the duration of the first pulse signal, wherein a midpoint timing Tm between the third timing Ts and the fourth timing Te occurs after 2.25T to 2.75T from the second timing Tp.   
     
     
       2. A method according to claim 1, wherein the duration of the second pulse signal is in a range from 0.3T to 2.0T. 
     
     
       3. A method according to claim 2, wherein the duration of the second pulse signal is preferably in a range from 0.5T to 0.7T. 
     
     
       4. A method according to claim 2, wherein the duration of the second pulse signal is preferably in a range from 1.3T to 1.7T. 
     
     
       5. A method according to claim 4, wherein the duration of the second pulse signal is more preferably 1.5T. 
     
     
       6. A method according to claim 1, wherein the midpoint timing Tm occurs after 2.5T from the second timing Tp. 
     
     
       7. A method according to claim 2, wherein steps (a) through (d) are executable at a frequency ranging from 5 kHz to 15 kHz. 
     
     
       8. A method according to claim 1, wherein the actuator is in the form of a wall defining the ink channel, at least a portion of the actuator being formed from a piezoelectric material. 
     
     
       9. A method of driving an ink ejection device having walls, a nozzle plate, an actuator and control means, the walls defining an ink channel, the ink channel having a volume filled with ink and having a length defined by two ends, the nozzle plate attached to one end of the ink channel and formed with a nozzle, the actuator operable for changing the volume of the ink channel and the control means, operable in association with a single power source, for applying pulse signals to the actuator, the method comprising the steps of: (a) applying a first pulse signal to the actuator at a first timing To so that the volume of the ink channel is increased from a natural volume to an increased volume, the first pulse signal having a voltage level, wherein a pressure wave is generated in the ink filing the ink channel, a time duration T being required for the pressure wave to propagate from one end to the other end in a lengthwise direction of the ink channel;   (b) stopping the application of the first pulse signal to the actuator at a second timing Tp after expiration the time duration T so that the volume of the ink chamber reverts to the natural volume, thereby ejecting an ink droplet from the nozzle, a duration of the first pulse signal being defined by a duration of time from the first timing To to the second timing Tp;   (c) applying a second pulse signal to the actuator so that pressure fluctuations remaining in the ink are canceled out, the second pulse signal having a voltage level equal to the voltage level of the first pulse signal; and   (d) stopping the application of the second pulse signal to the actuator at a fourth timing Te, a duration of the second pulse signal being defined by a duration of time from the third timing Ts to the fourth timing Te and differing from the duration of the first pulse signal, wherein a midpoint timing Tm between the third timing Ts and the fourth timing Te occurs after a duration of time longer than 3.20T but shorter than 3.75T from the first timing To.   
     
     
       10. A method according to claim 9, wherein the duration of the second pulse signal is in a range from 0.3T to 1.7T excluding 1.0T. 
     
     
       11. A method according to claim 9, wherein the midpoint timing Tm between the third timing Ts and the fourth timing Te occurs after a duration of time longer than 3.3T but shorter than 3.6T from the first timing To. 
     
     
       12. A method according to claim 11, wherein the duration of the second pulse signal is 0.5T. 
     
     
       13. A method according to claim 11, wherein the duration of the second pulse signal is preferably 1.5T. 
     
     
       14. A method according to claim 10, wherein steps (a) through (d) are executable at a frequency ranging from 5 kHz to 15 kHz. 
     
     
       15. A method according to claim 9, wherein the actuator is in the form of a wall defining the ink channel, at least a portion of the actuator being formed from a piezoelectric material.